1. Field of the Invention
The present invention relates to an exposure method, an exposure apparatus, and a method of manufacturing a device by using the exposure apparatus.
2. Description of the Related Art
In a projection exposure apparatus, when environment conditions such as atmospheric pressure, temperature, and humidity vary, the imaging characteristics of a projection optical system change. With recent miniaturization of semiconductor devices, demands have arisen for increases in the accuracy of imaging characteristics influenced by variations in environment conditions. This makes it necessary to correct the imaging characteristics. For example, Japanese Patent Laid-Open No. 7-183210 discloses a method of correcting changes in imaging characteristics due to variations in environment conditions. Japanese Patent Laid-Open No. 7-183210 discloses a method of detecting a change in atmospheric pressure as one of environment conditions and correcting changes in projection magnification and focus position with the change in atmospheric pressure by driving an optical member in a projection optical system in the optical axis direction. Letting ΔP be an atmospheric pressure change and K be an atmospheric pressure correction coefficient for a projection magnification, a projection magnification change ΔMP due to an atmospheric pressure change can be expressed byΔMP=Km×LP  (1)where KM is the coefficient determined by the characteristics of the projection optical system. This technique corrects imaging characteristics by calculating the driving amount of the projection optical system in the optical axis direction from ΔMP calculated by using equation (1).
The amount of change in aberration per unit atmospheric pressure is constant. However, the diffracted light intensity distribution within the pupil plane varies depending on the effective light source of an illumination optical system (the light intensity distribution in the pupil plane), the numerical aperture of a projection optical system, a mask, and conditions for the pattern of the mask. For this reason, changes in imaging characteristics due to changes in atmospheric pressure differ for the respective conditions described above. The same applies to changes in imaging characteristics accompanying the above changes in atmospheric pressure. If, therefore, the correction coefficient KM described above is uniquely determined regardless of the effective light source of the illumination optical system, the numerical aperture of the projection optical system, and the pattern of a mask, it is impossible to accurately correct changes in imaging characteristics due to changes in atmospheric pressure.